The field of this invention is variable speed fan drive systems and the like.
In the transportation of natural gas it frequently becomes necessary to increase the pressure of the gas in the gas transmission line to facilitate movement of the gas along the transmission line. Reciprocating piston and rotary compressors are commonly used to compress the gas and increase its pressure. This operation generates large amounts of heat which need to be dissipated. When the gas is compressed, its temperature increases appreciably. Additionally, heat must also be dissipated from the compressor cooling water and engine lubricants. One way in which heat is dissipated from the gas, lubricants, and cooling water is to pass those substances through separate finned, multiple tube banks and circulate air over the exposed areas of these finned tubes. Heat is thus transferred from the gas, lubricants, and cooling water, through the finned tubes, and to the environment.
Rotating fans are used to circulate air around the finned tubes. These fans are driven by a drive means, the power for which can be derived from the main compressor prime mover or from some external source. Regardless of its source, however, the power is transmitted to the fans through mechanical, electrical or hydraulic drives.
Several disadvantages were associated with known fan drive systems. Typically, they were not easily adjustable to vary the amount of air the fans passes over the finned tubes to account for ambient temperature differences between seasons. With many known fan drive systems, to adjust the amount of air passed over the finned tubes, it was necessary to shut down the compressor which served as the prime mover for the drive system and to manually change the pitch of the fan blades. This process was undesirable not only because it caused an interruption in the gas compressor output, but also because the adjustments resulted in a waste of energy. Adjusting the pitch of the fan blades merely amounted to spilling a part of the horsepower developed by the compressor in order to set the fan speed. This spilling of the excess horsepower was, of course, a waste of energy. Spilling the horsepower from the compressor also reduced the amount of compressor horsepower available to accomplish the work of compressing gas.
Further, with mechanically driven systems, the location of the fan drive means relative to the prime mover was severely limited.